Gas sensor and gas sensor unit

Abstract

A gas sensor including a detection element having a detection portion; a metal shell that surrounds the detection element so as to expose the detection portion to a measured atmosphere; an outer tube that is fixed to the metal shell so as to cover a rear end side of the detection element; and a seal member that is contained inside the outer tube, the seal member having a lead wire insertion hole and a through hole that penetrates in the axial direction; a tubular holding member made of a resin having a lower coefficient of thermal expansion than the seal member, the tubular holding member being held inside the through hole, the tubular holding member having a ventilation hole; and a filter that covers the ventilation hole, the filter being joined to the holding member, the filter blocking water from passing therethrough, and the filter having air permeability.

1. A gas sensor comprising:
 a detection element that extends in an axial direction, the detection element having a detection portion that detects a concentration of a specific gas in a measured atmosphere, the detection portion being positioned in a leading end side of the detection element; 
 a metal shell that surrounds the detection element so as to expose the detection portion to the measured atmosphere; 
 an outer tube that is fixed to the metal shell so as to cover a rear end side of the detection element; and 
 a seal member that is contained inside the outer tube, the seal member having a lead wire insertion hole into which a lead wire is inserted for electrically connecting the detection element and an external device and a through hole that penetrates in the axial direction, 
 the gas sensor further comprising: 
 a tubular holding member made of a resin having a lower coefficient of thermal expansion than the seal member, the holding member being held inside the through hole, the holding member having a ventilation hole that introduces a gas into an inside of the outer tube; 
 a filter that covers the ventilation hole, the filter being joined to the holding member, the filter blocking water from passing therethrough, and the filter having air permeability; and 
 a mesh that covers the filter from a rear end side, the mesh being made of metal or a resin having air permeability, wherein the mesh has a higher air permeability than the filter. 
 
     
     
       2. The gas sensor according to  claim 1 ,
 wherein the filter is welded onto the holding member. 
 
     
     
       3. The gas sensor according to  claim 1 ,
 wherein the holding member has a concave portion protruding outwardly in a radial direction from the ventilation hole, and 
 wherein the filter and the mesh are nipped in the concave portion. 
 
     
     
       4. The gas sensor according to  claim 1 , further comprising,
 a covering member that covers the holding member from the rear end side so as to cover the filter held by the holding member, 
 wherein the covering member has the mesh at the position covering the filter. 
 
     
     
       5. The gas sensor according to  claim 1 ,
 wherein the mesh and the holding member are directly joined to each other by the welding. 
 
     
     
       6. The gas sensor according to  claim 5 ,
 wherein the mesh and the filter are spaced apart from each other. 
 
     
     
       7. The gas sensor according to  claim 5 ,
 wherein the holding member has an outer wall protruding in the axial direction along its circumference and a depression surrounded by the outer wall, 
 wherein the filter is disposed in the depression, and 
 wherein the mesh is joined to the outer wall. 
 
     
     
       8. The gas sensor according to  claim 7 ,
 wherein the outer wall is provided with protrusions protruding in the axial direction and disposed at a constant interval along its circumference, and 
 wherein the mesh is joined to the protrusions. 
 
     
     
       9. A gas sensor unit comprising:
 a detection element having a detection portion which detects a concentration of a specific gas in a measured atmosphere, the detection portion being positioned in a leading end side of the detection element; 
 a gas sensor having a sensor terminal which is electrically connected to the detection portion and which transmits a signal output from the detection element; 
 a sensor cap that is combined with the gas sensor, the sensor cap comprising: 
 a cap terminal which is electrically connected to the sensor terminal; and 
 an envelopment member, which surrounds the cap terminal, which is combined with the gas sensor to form an inside space between the gas sensor and the envelopment member, the envelopment member having a through hole which establishes communication between the inside space and external atmosphere, 
 the sensor cap transmits the output signal to an external device, and 
 wherein the gas sensor unit further comprises: 
 a tubular holding member that is made of resin having a lower coefficient of thermal expansion than the envelopment member, the holding member being held inside the through hole, and the holding member having a ventilation hole that introduces a gas inside the envelopment member; 
 a filter that covers the ventilation hole, the filter being joined to the holding member, the filter blocking water from passing therethrough, and the filter having air permeability; and 
 a mesh that covers the filter from a rear end side, the mesh being made of metal or a resin having air permeability, wherein the mesh has a higher air permeability than the filter. 
 
     
     
       10. The gas sensor unit according to  claim 9 ,
 wherein the filter is joined to the holding member by welding. 
 
     
     
       11. The gas sensor unit according to  claim 9 ,
 wherein the holding member is provided with a concave portion protruding in a radial direction of the ventilation hole from the ventilation hole, and 
 wherein the filter and the mesh are nipped in the concave portion. 
 
     
     
       12. The gas sensor unit according to  claim 9 , further comprising,
 a covering member that covers the holding member from a rear end side so as to cover the filter held by the holding member, 
 wherein the covering member has the mesh at the position covering the filter. 
 
     
     
       13. The gas sensor unit according to  claim 9 ,
 wherein the mesh and the holding member are directly joined to each other by the welding. 
 
     
     
       14. The gas sensor unit according to  claim 13 ,
 wherein the mesh and the filter are spaced apart from each other. 
 
     
     
       15. The gas sensor unit according to  claim 13 ,
 wherein the holding member has an outer wall protruding in a penetrating direction of the ventilation hole over a circumference of the outer wall and a depression surrounded by the outer wall, 
 wherein the filter is disposed in the depression, and 
 wherein the mesh is joined to the outer wall. 
 
     
     
       16. The gas sensor unit according to  claim 15 ,
 wherein the outer wall is provided with protrusions protruding in the penetrating direction of the ventilation hole and disposed at a constant interval over a circumference of the outer wall, and 
 wherein the mesh is joined to the protrusions.